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Friends look at the world in similar ways, brain-scan study suggests

Researchers found that the neural activity of friends’ brains was more similar than that of people who knew each other less well, particularly in brain regions involved in emotion, attention and high-level reasoning.

It’s possible to predict whom people are friends with by observing their brain activity as they watch video clips, reports a new study from Dartmouth College.

Friends are more likely to have similar neural responses to the clips than friends-of-friends, the study found. And friends-of-friends have responses that are more alike than people separated by yet another degree (friends-of-friends-of-friends).

These findings add neuroscientific support to the idea that friendships — and larger social networks — are formed among people who share similar perceptions of the world.

“Neural responses to dynamic, naturalistic stimuli, like videos, can give us a window into people’s unconstrained, spontaneous thought processes as they unfold,” said lead author Carolyn Parkinson in a released statement. “Our results suggest that friends process the world around them in exceptionally similar ways.” Parkinson, who was a postdoctoral researcher in psychological and brain sciences at Dartmouth while working on the study, is currently an assistant professor of psychology at the University of California, Los Angeles.

The study was published this week in the journal Nature Communications.

Study details

For the study, Parkinson and her colleagues asked all 279 first-year graduate students in one of Dartmouth’s programs to identify which of the other students in the program were their friends, or friends of their friends, or friends of their friends’ friends.

A “friend” was defined as somebody you’d go out with for a movie, a meal or other “informal social activity.” Any two students who named each other as friends were considered such for the purposes of the study.

Using all the answers, the researchers mapped the social ties of the entire group of students.

Forty-two of the students were then asked to watch short videos on various topics and in several genres — including politics, science, comedy and music — while their brain activity was recorded using a functional magnetic resonance imaging (fMRI) scanner. The videos were selected to elicit a range of responses. A political video, for example, might raise anger in some people, but not in others. Each person watched the same videos in the same order.

The researchers compared scans from pairs of students to see how closely they resembled each other. They found that the neural activity of friends’ brains was more similar than that of people who knew each other less well, particularly in brain regions involved in emotion, attention and high-level reasoning.

The similarities were so “striking,” said the researchers, that they could use the brain scans to not only predict whether two people were friends, but also the social distance between them.

"These results suggest that we are exceptionally similar to our friends in how we perceive and respond to the world around us," the researchers write in their paper.

A major caveat

The research comes with several limitations, of course. The biggest caveat is that it looked only at a friendship network within a graduate program at a single university. The selection of friends in such a program may not reflect how people choose their friends in other environments.

Still, other evidence also suggests that our choice of friends may be hardwired within us. Other research has found that the friends of both adults and teens tend to be more genetically similar than random pairs of people. 

The Dartmouth researchers’ next step, they say, is to investigate whether people naturally gravitate toward others who see the world as they do or if the similarities develop after individuals meet and share experiences.

FMI: The study can be read in full on the Nature Communications website.

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